@luckystar Hopefully you've found a little relief since you wrote this. In case you still read these forums...
Just wondering why you guys are letting the Ex get away with all of the violations regarding visitation? Is it a matter of not wanting to spend the money to take her to court? Are you documenting in a journal of some kind? There are plenty of mental health terms applied to toxic Ex wives and husbands but you don't need a diagnosis and it's darned near impossible to get one anyway. Abuse is abuse no matter what label you put on it. You guys don't have to suffer. Use the high conflict strategies out there for dealing with her if you feel like that is your situation.
I'd minimize your interactions with her. Sadly the stereotype of the Ex wife hating the new woman rings true for many. It just serves to add fuel to their ire. It's not fair and reasonable adults should be able to set aside emotion for what's in the best interest of the kids but sometimes it doesn't work out. Obviously you and your hubby are partners now and you make decisions together. Legally only those two are able to make decisions regarding the children. She has no legal reason to talk to you at all.
If you have a question for her get him to ask it. Better yet set up your lives to minimize any questions. You can avoid things like "where is little Johnny's stuffed animal?" just by keeping your own set of toys that don't go to mom's house. Talk to teacher's directly to get progress reports. It's a total PIA to do it that way but you'll be grateful for the peace that approach provides you over time. My partner never gives our Ex a response when he is conversing with her because he comes back to discuss it with me first. That is our boundary and our rules. Our Ex knows that. She doesn't want me involved in the discussions so she has to wait a little longer to get her answers.
The co-parenting approach is a social construct only. Remember she doesn't have to play nice with you if she doesn't want to. It's best for the kids if she does but it is not a legal requirement. To minimize conflict he should be the front man with all communication. My experience is the bad feelings dropped tremendously when we went that route with our Ex. Try to think of it in a compassionate way. You've got him, she's got the memories and there is pain there and likely every time she deals with you it is a reminder. It's not your fault and there really is no way for you to heal her pain but just be compassionate. This will eventually pass. My Ex reaches out to me a lot more now than she did when I was actually trying to work with her.